Background: Pulmonary tuberculosis (TB) is a growing public health problem, and detection is often costly and time-consuming. A breath test for volatile markers of Mycobacteria could provide a new test for the disease. An advanced new breath test routinely detects volatile organic compounds (VOCs) in breath in picomolar (10-12 mol/l) concentrations. M. tuberculosis manufactures volatile fatty acids and other volatile metabolites; detection of these VOCs in breath could provide an accurate, rapid, inexpensive and non-invasive new marker of infection in patients with active pulmonary TB. Experimental plan: In vitro study: Volatile metabolites in cultures of M. tuberculosis will be identified by gas chromatography and mass spectroscopy. Human study: In patients evaluated for suspected pulmonary TB, breath VOCs will be compared in those with and without disease. The sensitivity, specificity, and positive and negative predictive values of the breath test will be determined. Long term aims: a. Scientific: To determine the diagnostic accuracy of breath markers of M. tuberculosis. b. Technical: to develop a comparatively inexpensive miniaturized and rapid breath test suitable for clinical use and in less developed countries. c. Commercial: To obtain Food and Drug Administration (FDA) approval of the device and market it.